Coating compositions based on acrylic polymers and aminoplast crosslinking agent are particularly desirable as automotive top coats because they have excellent durability, hardness, gloss and appearance. However, such coating compositions, when used as clear coats in color plus clear composite coatings, are particularly susceptible to acid etching. Acid etching is a phenomenon associated with acidic rain water, which is common in many urban and industrial areas. When acidic rain water, also known as acid rain, accumulates on a horizontal section of an automobile such as a hood or trunk deck, it spots and can actually etch away the clear coat leaving a blemish that cannot be polished out. It has been found that acrylic polymers containing pendant or terminal carbamate groups can be cured with aminoplast crosslinking agents to give acid etch resistant clear coats. Publications that disclose such polymers are U.S. Pat. No. 5,356,669, U.S. Pat. No. 5,336,566, EPO 0,594,142 A1 and EPO 0,590,068 A1.
A problem associated with curable coating compositions based on acrylic polymers containing pendant carbamate groups and aminoplast curing agents is that the compositions do not have particularly good intercoat adhesion. This problem presents itself when the compositions are used as clear coats in composite color plus clear composite coatings, especially during repair procedures which involve applying the clear film-forming composition to a flawed area of a previously applied color plus clear composite coating. The clear coats can actually delaminate from underlying layers of film.